London Irish beat Munster 23-19 in their opening Pool Three clash, but won't be happy the visitors bagged a crucial losing bonus point at the death in a thrilling Heineken Cup encounter.
Top of the Aviva Premiership got the better of top of the Magners League.
English sides have struggled to cope with the intensity and physicality of the top Irish sides in recent seasons, but London Irish proved more than a match for the two-time former champions.
But their evening will have been soured somewhat by the final play of the night, as Munster came up with a last-gasp try almost from nowhere. That losing bonus point could ultimately prove vital.
This was not the awesome Munster of old - missing Paul O'Connell their forwards lacked their customary dominance and their line-out, while not exactly struggling, certainly creaked.
As for Irish, this display will give them great confidence of emerging from probably the competition's toughest group, one which also includes Toulon and Ospreys.
Their victory was built around a solid forward display and the clever prompting of fly-half Ryan Lamb, who got the better of Munster veteran Ronan O'Gara - at least until the final minute.
Try-scoring opportunities were at a premium for both sides, with Munster looking to set up chances for O'Gara's boot. The Exiles were happy to play a similar game and trust in Lamb's goal-kicking.
London Irish also had the better of the contact area, winning a string of penalties as Munster hung on to the ball or failed to roll away.
Munster did make a bright start and took a deserved lead when their early pressure forced a penalty and O'Gara duly knocked over the kick.
But the rest of the half saw London Irish predominantly on the front foot, helped by Sam Tuitupou's 10-minute absence midway through the half for a spear tackle.
They did not threaten the Munster line but did force penalties, Lamb kicking four and a drop-goal in the closing moments, although the visitors had the final say as O'Gara cut the half-time deficit to 15-6.
But London Irish extended that within 30 seconds of the re-start, Johne Murphy's short inside pass on the counter juggled and intercepted by Topsy Ojo, who raced 50 metres to score in the corner.
Lamb missed the conversion from out wide and O'Gara kicked a penalty after Munster forced a scrum-collapse, before putting his next penalty into the corner on the hour mark.
The Munster forwards battered away at the defence in time-honoured fashion and got to within half a metre of the line. Prop Tony Buckley looked set to crash over, but Delon Armitage came up with a superb tackle and a knock-on saved the Exiles.
O'Gara did go for the kick on 68 minutes and cut the lead to 20-12, but Armitage attempted a penalty from inside his own half and made it.
That should have been that, but Munster were deteremined to battle to the end and duly got their reward. David Wallace burst up the centre to open up the defence and O'Gara's perfectly-weighted chip was touched down by Tuitupou.
For London Irish:
Pens: Lamb 4, Armitage
Pens: O'Gara 4
London Irish: 15 Delon Armitage, 14 Topsy Ojo, 13 Elvis Seveali'i, 12 Seilala Mapusua, 11 Sailosi Tagicakibau, 10 Ryan Lamb, 9 Paul Hodgson, 8 George Stowers, 7 Declan Danaher, 6 Kieran Roche, 5 Bob Casey, 4 Nick Kennedy, 3 Faan Rautenbach, 2 James Buckland, 1. Clarke Dermody (capt)
Replacements: 16. David Paice, 17 Max Lahiff, 18 Alex Corbisiero, 19 Matt Garvey, 20 Chris Hala'ufia, 21 Jonathan Joseph, 22 Daniel Bowden, 23 Darren Allinson
Munster: 15 Johne Murphy, 14 Doug Howlett, 13 Keith Earls, 12 Sam Tuitupou, 11 Denis Hurley, 10 Ronan O'Gara, 9 Peter Stringer, 8 James Coughlan, 7 Niall Ronan, 6 Denis Leamy (capt), 5 Donnacha Ryan, 4 Donncha O'Callaghan, 3 Tony Buckley, 2 Damien Varley, 1 Wian du Preez
Replacements: 16 Mike Sherry, 17 Marcus Horan, 18 John Hayes, 19 Mick O'Driscoll, 20 David Wallace, 21 Duncan Williams, 22 Paul Warwick, 23 Scott Deasy
Referee: Christophe Berdos